2004 Dodge Durango AIr Horn?

[David N]

Hi Im a Volunteer Fireman and I want to buy a PA/Air Horn for my car. The model of the PA/Air Horn is the Whelen WHPAP 112. I want to wire air horn to my regular horn so when the air horn is on pushing the regular horn will use the air horn tone and when the air horn is off pushing the horn will use the regular horn tone. I know it has something to do do with the horn ring and horn relay circuit but I don't know where it is in my car. Does anyone know where the horn ring and the horn relay circuit is? Thanks David